1. Field of the Invention
The present invention relates to a processing enzyme for a polypeptide, more particularly, to an enzyme which converts a precursor of a polypeptide that induces interferon-.gamma. (hereinafter abbreviated as "IFN-.gamma.") production in immunocompetent cells into the active form.
2. Description of the Prior Art
The present inventors succeeded in isolating a polypeptide which induces IFN-.gamma. production in immunocompetent cells and a cDNA encoding the polypeptide, and disclosed them in Japanese Patent Kokai Nos.27,198/96 and 193,098/96.
The polypeptide is featured in inducing the production of IFN-.gamma. as a useful biologically active substance, enhancing the cytotoxicity by killer cells, and inducing the formation of killer cells; it can be expected for use as anti-virus agents, antiseptics, antitumor agents and anti-immunopathy agents.
It is said that, in human cells, polypeptides formed by gene expression may be processed by intracellular enzymes to partially digest the polypeptides and add sugar chains thereunto.
Polypeptides to be satisfactorily incorporated into pharmaceuticals may be those which received processings similarly as in human cells; such cells have a demerit that they less produce the present polypeptide as disclosed in Japanese Patent Application No.269,105/96. The present inventors' energetic study revealed that the polypeptide usually exists in human cells in the form of a precursor with a molecular weight of about 24,000 daltons and no biological activity. Although it is not restricted to the polypeptide, it is known that most cytokines are usually produced as precursors with no biological activity, and then processed by intracellular enzymes to be converted into their active forms.